The present invention relates generally to the field of substrate processing for semiconductor manufacturing and, more specifically, to lamp arrays for thermal processing chambers.
An important part of integrated circuit manufacturing is processing of the semiconductor substrate in which active devices such as transistors and capacitors that comprise the integrated circuit are formed. Processing of the substrate includes growth of an epitaxial silicion or polysilicon layer, the formation of a thermal oxide or thermal nitride layer over silicon, or etching of portions of previously deposited layers. These exemplary processes are typically performed in thermal process chambers. Process chambers typically include a platform such as a susceptor or an edge ring, a substrate support mechanism, a quartz housing or cover, and an array of lamps that provide radiant heat energy to the interior of the chamber and the substrate being processed.
The semiconductor substrate is typically in a form of a generally round silicon wafer that rests on a top surface or in a pocket of a substrate holding platform. The substrate holding platform is typically inside of a generally rectangular chamber housing. The gas flow is provided from one end of the chamber to the other end of the chamber. The process gas is injected into the chamber across the width of the chamber such that the process gas forms a rectangular flow field across the generally round substrate.
Deposition and etching are typically performed in thermal processing chambers by flowing gases that include certain chemical species over the heated substrate surface. The chemical species react at the substrate surface to deposit layers of material onto the substrate or to etch portions of layers of material from the substrate. The process chamber typically includes a gas inlet port at one end and a gas outlet port at an opposite end.
The array of lamps provides radiant heat energy to the water or sutstrate such that the chemical species in the process gas react at the wafer surface. The deposition reaction results in a change in the process gas composition (i.e., depletion of the gas species) in the direction of the gas flow. For this reason, some chambers are provided with a mechanism to rotate the wafer holder that carries the substrate such that the reaction rate at the surface of the substrate is averaged out to provide uniformity of thickness of the deposition or of depth of etching along the entire surface.
Considerable effort has been expended toward the design of thermal processing chambers for semiconductor substrates in an effort to achieve improved uniformity of thickness of deposition on the surface of semiconductor substrates and uniformity of depth of etching of material from the substrate surface. For instance, various substrate holding trays and platforms that hold a substrate during processing have been designed to provide uniform and consistent heating of the substrate during processing. Also, rotation mechanisms have been provided to rotate the substrate holding platform during processing.
In order to achieve uniform process gas depletion, various heat sources have been designed. The design of the heat source of a thermal processing chamber can also have an effect on the uniformity of deposition or etching of the semiconductor substrate. A heat source such as a lamp array can provide heat uniformly across the width of a rectangular process chamber housing such that the process gas flow field is heated uniformly across such width. A rectangular heat pattern, however, does not provide an ideal thermal profile on a circular wafer because the rectangular heat profile is transposed on the circular profile of the substrate. The four edges of the rectangular heat pattern are therefore closer to the circular substrate at points near the middle of each edge while the corners of the rectangular heat pattern are further away from the circular substrate. Thus, the temperature profile of the circular substrate at areas closer to the corners of the rectangular heat pattern can be different than the temperature profile of the circular substrate at locations near the edges of the rectangular heat pattern.
In order to minimize the variation of the thermal profile of the substrate, generally circular heat sources have been developed. Circular heat sources more closely match the circular profile of the substrate, and therefore provide a more uniform temperature profile at all points of the circular substrate. A circular heat source, however, does not uniformly heat the process gas as it flows across the surface of the substrate in a rectangular flow field. The process gas is injected across the width of the rectangular process chamber and moves across the wafer. The process gas becomes heated at the leading edge of the circular wafer by the circular heat source. As the rectangular flow field of the process gas continues across the wafer, the heated zone becomes wider until the middle of the circular substrate is reached and then becomes narrower until the flow field proceeds completely across the substrate. As a result, the depletion of the process gas is greater over the central diameter of the substrate (parallel to the gas flow direction) because that portion of the process gas is heated over a longer period of time than a portion of the process gas that crosses a shorter chord of the circular profile of the substrate.
In an attempt to overcome the non-uniform depletion effects of a circular heat source and also the non-uniform thermal profile resulting from a rectangular heat source, considerable effort has been made to provide mechanisms by which the substrate is rotated or tilted in order to exploit the depletion effects of the process gas. Additional mechanism or process steps, however, introduce process variables that can potentially cause defects if not controlled within required process parameters.
In one embodiment, a lamp array for a thermal processing chamber includes a plurality of lamps arranged in at least two concentric rings. In other embodiments, corner lamp arrays are positioned around the circumference of a circular lamp array to provide a generally rectangular heating pattern. In yet other embodiments, rows of end lamps can be positioned tangentially with respect to the circular portion of a lamp array to provide preheating and postheating of processes gases.